Two aircraft narrowly avoided a mid-air crash over Ireland West Airport last year, an investigation has found.

The planes were carrying out technical checks at the same time over the same runway at the Knock airport, in Co Mayo, when they came within just hundreds of metres of each other.

Air accident investigators said one of the planes was forced to make a last ditch manoeuvre to avoid collision - but it was already too late and it was only "fortuitous" that there was not a serious incident.

During the near miss, one of the air traffic controllers was recorded as saying: "It's kinda very unusual for us to have both of ye here at the same day."

The Air Accident Investigation Unit (AAIU) has slammed a lack of communication and co-ordination for allowing the two maintenance flights - each carrying two crew and a flight inspector - to carry out aerial work over the same runway at the same time.

The report found Ireland West Airport had brought in a private UK company to carry out technical checks on its navigational aids on April 22 last year.

Air traffic controllers were not told that the Irish Aviation Authority had ordered another private UK company to also complete similar checks on the same runway that day.

Investigators said airport technical chiefs did not give prior notification to traffic control about the other maintenance flight.

At one stage, the Diamond Twin Star aircraft came within 0.42 nautical miles - or 700 metres - of the Piper plane and neither could see each until the 62-year-old commander of the Diamond Twin Star carried out a manoeuvre to avoid a crash.

The situation was made worse because of clouds and there was no radar equipment at the airport at the time, it was found.

"In this particular case, a sequence of events led to a situation whereby two calibration aircraft operating towards and across the same runway approach at (Ireland West Airport) narrowly avoided a collision," the air accident report said.